USPTO Patents Application 09840196

INFLATABLE SIDE CURTAIN WITH FILL TUBE

Cross Reference to Related Applications

This application is a continuation-in-part of U.S.

502. ^ _ _ _

Application No. 0 9/2-0-5,83 8, which was filed on February

11, 2 000.

A

Field of the Invention

The present invention relates to an inflatable
apparatus for helping to protect a vehicle occupant in
the event of a side impact to a vehicle and/or a
vehicle rollover.

Background of the Invention

It is known to inflate an inflatable vehicle
occupant protection device to help protect a vehicle
occupant in the event of a vehicle collision. One
particular type of inflatable vehicle occupant
protection device is an inflatable curtain that
inflates from adjacent the. roof of the vehicle downward

inside the passenger compartment between a vehicle
occupant and the side structure of the vehicle in the
event of a side impact or rollover. A known inflatable
curtain is inflated from a deflated condition by
inflation fluid directed from an inflator to the
inflatable, curtain through a fill tube.

Summary of the Invention

The present invention relates to an apparatus for
helping to protect an occupant of a vehicle that has a
side structure and a roof. The apparatus comprises an
inflatable vehicle occupant protection device that is
inflatable away from the roof into a position between
the side structure of the vehicle and a vehicle
occupant . The inflatable vehicle occupant protection
device defines an inflatable volume and has a length
extending along the side structure of the vehicle. The
inflatable volume includes a forward portion located
forward in the vehicle and a rearward portion located
rearward in the vehicle.

An inflation fluid source provides inflation fluid
for inflating the inflatable vehicle occupant
protection device. The inflation fluid consists
essentially of helium. A fill tube has a portion
located in the inflatable vehicle occupant protection

device that extends into the forward portion and the
rearward portion of the inflatable volume. The fill
tube is in fluid communication with the inflation fluid
source. The inflation fluid source, when actuated,
provides inflation fluid to the fill tube. The fill
tube includes outlet apertures positioned along the
portion of the fill tube that direct the inflation
fluid into the inflatable volume to inflate the
inflatable vehicle occupant protection device initially
to a first desired pressure and maintain the inflatable
vehicle occupant protection device inflated above a
second desired pressure for a predetermined period of
time. The predetermined period of time is at least 5-7
seconds .

The inflation fluid is directed through the outlet
apertures into the forward portion and the rearward
portion of the inflatable volume to inflate the forward
and rearward portions. The inflation fluid directed
into the forward portion and the inflation fluid
directed into the rearward portion have generally the
same temperature and a generally the same pressure
during initial inflation of the inflatable vehicle
occupant protection device. The temperature of the
inflation fluid directed into the forward and rearward

potions is about equal to an ambient temperature in
which the inflatable vehicle occupant protection device
is inflated for at least 95% of the predetermined
period of time.

Brief Description of the Drawings

The foregoing and other features of the, present
invention will become apparent to one skilled in the
art to which the present invention relates upon
consideration of the following description of the
invention with reference to the accompanying drawings,
in which:

Fig. 1 is a schematic view of an inflatable
apparatus for helping to protect an occupant of a
vehicle according to the present invention illustrating
the apparatus in a deflated condition;

Fig. 2 is a schematic view of the apparatus of
Fig, 1 in an inflated condition;

Fig. 3 is a sectional view of the apparatus taken
generally along line 3-3 in Fig. 2;

Fig. 4 is a sectional view of the apparatus taken
generally along line 4-4 in Fig. 2;

Fig. 5 is a schematic view of a portion of the
apparatus of Fig . 1 ;

Fig. 6 illustrates a model curtain for simulating
the performance of the apparatus of Fig. 1 ;

Figs. 7a-b and 8a-b are graphs illustrating the
performance of the model curtain of Fig. 6;

Fig. 9 illustrates a model curtain for simulating
the performance of an apparatus similar to the
apparatus of Fig. 6 having certain features omitted;

Figs. 10-11 are graphs illustrating the
performance of the model curtain of Fig. 9;

Fig. 12 illustrates a model curtain for simulating
the performance of an apparatus similar to the
apparatus of Fig. 6 having certain features omitted and
other features added;

Figs. 13-14 are graphs illustrating the
performance of the model curtain of Fig. 12; and

Figs. 15-18 are graphs illustrating actual
measured performance of an inflatable curtain in
accordance with the apparatus of Fig. 1.

Description of Preferred Embodiments

As representative of the present invention, an
apparatus 10 helps to protect an occupant of a
vehicle 12. As shown in Figs. 1 and 2, the
apparatus 10 includes an inflatable vehicle occupant
protection device in the form of an inflatable

curtain 14 that is mounted adjacent the side
structure 16 of the vehicle 12 and a roof 18 of the
vehicle. The side structure 16 of the vehicle 12
includes side windows 20. An inflator 24 is connected
in fluid communication with the inflatable curtain 14
through a fill tube 22. The inflator 24 contains a
stored quantity of pressurized helium inflation fluid
(not shown) for inflating the inflatable curtain 14.

The fill tube 22 has a first portion 30 for
receiving fluid from the inflator 24. The fill tube 22
has a- second portion 32 di-sposed in the ±nf Tatablei
curtain 14. The second portion 32 of the fill tube 22
has a plurality of openings (not shown in Figs. 1
and 2) that provide fluid communication between the
fill tube 22 and the inflatable curtain 14.

The apparatus 10 includes a housing 2 6 (Fig. 1)
that stores the inflatable curtain 14 in a deflated
condition. The fill tube 22, the deflated inflatable
curtain 14, and housing 26 have an elongated
configuration and extend along the vehicle roof 18 and
along the side structure 16 of the vehicle 12 above the
side windows 20. The roof 18 may be either a standard
roof that is fixed in place or a convertible roof that
can be moved or removed.

As best illustrated in Fig. 3, the inflatable
curtain 14 comprises first and second panels 40 and 42
that are arranged in an overlying manner. Overlapping
portions 44 of the first and second panels 40 and 42
are secured together by stitching 46 (Figs. 2 and 3)
that extends along at least a portion of the perimeter
48 of the panels. The overlapping portions 44 could
alternatively be secured together by means such as
dielectric sealing, ultrasonic bonding, heat sealing,
or adhesives. The perimeter 48 is defined at least
partially by an uppe-r^ edge 50 (Fig. 2~) of the
inflatable curtain 14, an opposite lower edge 52 of the
curtain, and front and rear edges 54 and 5 6 of the
curtain spaced apart horizontally along the upper and
lower edges. The perimeter 48 defines an inflatable
volume 58 of the inflatable curtain 14. Although the
upper and lower edges 50 and 52 and the front and rear
edges 54 and 56 are shown as straight lines, the upper
and lower edges could be curved or angled. The upper
and lower edges 50 and 52 thus might intersect and
eliminate either or both of the front and rear edges 54
and 5 6 .

In the illustrated embodiment, the inflatable
curtain 14 (Fig. 3) is formed from a sheet of material

that is folded over to form the overlying first and
second panels 40 and 42. It will be recognized by
those skilled in the art, however, that the inflatable
curtain 14 could have alternative constructions. For
example, the first and second panels 40 and 42 could be
formed from separate sheets of material arranged in an
overlying manner and secured together by stitching 46
that extends around the entire perimeter 4 8 of the
panels. The first and second panels 40 and 42 may also
be woven together around their perimeters to form the
inflatable curtain 14.

The first and second panels 40 and 42 are
constructed of a fabric, such as nylon, that is coated
with a gas impermeable material, such as urethane or
silicone. The inflatable curtain 14 thus may have a
substantially gas-tight construction. Other materials,
such as elastomers, plastic films, or combinations
thereof, may also be used to construct the inflatable
curtain 14. The first and second panels 40 and 42 may
also be formed of single or multi-layered sheets of
material .

As illustrated in Fig. 4, the first and second
panels 4 0 and 42 may be connected together by known
means 60, such as stitching, dielectric sealing,

ultrasonic bonding, heat sealing, adhesives, tethers,
or weaving the panels together, to form a non-
inflatable area 62 within the inflatable volume 58
(Fig. 2) of the inflatable curtain 14. Such a non-
inflatable area 62 may be desirable in areas along the
side structure 16 of the vehicle 12 where occupants are
unlikely to come into contact with the side structure.
This may help to reduce the amount of inflation fluid
required to fill the inflatable curtain 14 and reduce
the time required to inflate the curtain. Such a non-
inflatable area 62 may also be desirable to help
control the thickness of the inflatable curtain 14 and
to define inflatable chambers of the curtain.

As illustrated in Fig. 2, the non-inflatable
area 62 is generally rectangular. It will be
recognized by those skilled in the art, however, that
it may be desirable for the non-inflatable area 62 to
have a different configuration, depending upon the
particular design of the inflatable curtain 14, the
shape of the vehicle 12 in which the apparatus 10 is
being installed, and the desired shape of the
inflatable portion (s) of the curtain. For example, the
non-inflatable area 62 could consist of linear
connections such that the panels are connected along

straight or curved lines, areas of connection such that
the curtain panels are connected together in areas
defined by straight or curved boundaries, or a
combination of linear connections and area connections.

In the illustrated embodiment, the non- inflatable
area 62 helps to define inflatable forward and rearward
portions 64 and 66, respectively, of the inflatable
volume 58 of the inflatable curtain 14 . In the
illustrated embodiment, the forward and rearward
portions 64 and 66 are connected in fluid communication
with each other by passages 68 that extend along the
upper and lower edges 50 and 52 of the inflatable
curtain 14 between the respective upper and lower edges
and the non- inflatable area 62. The forward and
rearward portions 64 and 66, however, may not be
connected in fluid communication with each other. When
the inflatable curtain 14 is inflated, the forward
portion 64 is positioned forwardly in the vehicle 12,
between the side structure 16 of the vehicle and any
occupants seated forwardly in the vehicle. The
inflated rearward portion 66 is positioned rearwardly
in the vehicle 12, between the side structure 16 of the
vehicle and any occupants seated rearwardly in the
vehicle .

The vehicle 12 includes a sensor mechanism 70
(shown schematically in Figs. 1 and 2) for sensing a
side impact to the vehicle 12 and/or a rollover of the
vehicle 12 . The sensor mechanism 70 actuates the
inflator 24 in response to the sensing of a side impact
or a vehicle rollover. In the event of a rollover of
the vehicle 12 or a side impact to the vehicle for
which inflation of the inflatable curtain 14 is
desired, the sensor mechanism 70 provides an electrical
signal over lead wires 72 to the inflator 24 . The
electrical signal causes the inflator 24 to be actuated
in a known manner. The inflator 24 discharges
inflation fluid under pressure into the fill tube 22 .
The fill tube 22 directs the inflation fluid into the
inflatable curtain 14.

The inflatable curtain 14 inflates under the
pressure of the inflation fluid from the inflator 24 .
The housing 2 6 (Fig. 1) opens and the inflatable
curtain 14 (Fig. 2) inflates away from the roof 18 in a
downward direction as shown in the drawings and in a
downward direction with respect to the direction of
forward travel of the vehicle 12 into the position
illustrated in Fig. 2.

The inflatable curtain 14, when inflated, extends
along the side structure 16 of the vehicle 12 and is
positioned between the side structure and any occupant
of the vehicle. When the inflatable curtain 14 is in
the inflated condition, the first panel 40 is
positioned adjacent the side structure 16 of the
vehicle 12 . The upper edge 50 of the inflatable
curtain 14 is positioned adjacent the intersection of
the roof 18 and the side structure 16 of the
vehicle 12 . The front edge 54 of the inflatable
curtain 14 is positioned adjacent an A pillar 80 of the
vehicle 12 . The rear edge 56 of the inflatable
curtain 14 is positioned adjacent a C pillar 82 of the
vehicle 12 . The inflatable curtain 14 extends between
the A pillar 80 and the C pillar 82 of the vehicle 12
and overlies at least a portion of the A pillar, C
pillar, and a B pillar 84 of the vehicle.

It will be recognized by those skilled in the art
that the inflatable curtain may have alternative
configurations. For example, in the illustrated
embodiment, the inflatable curtain 14 extends between
the A pillar 80 and the C pillar 82 of the vehicle 12.
The inflatable curtain 14 could, however, extend
between the A pillar 80 and the B pillar 84 only or

between the B pillar and the C pillar 82 only. Also,
the inflatable curtain 14 could, when inflated, extend
between the A pillar 80 and a D pillar 86 of the
vehicle 12 .

The inflatable curtain 14, when inflated, helps to
protect a vehicle occupant in the event of a vehicle
rollover or a side impact to the vehicle 12. The non-
inflatable portion 62 helps to limit the thickness of
the inflated inflatable curtain 14 and helps to reduce
the overall volume of the curtain. The forward and
rearward portions 64 and 66, when inflated, help to
absorb the energy of impacts with the inflatable
curtain 14 and help to distribute the impact energy
over a large area of the curtain. The passages 68 also
help to distribute the impact energy over a large area
of the inflatable curtain 14 by allowing inflation
fluid to move between the forward and rearward
portions 64 and 66 upon impacts with the curtain.

Once the inflatable curtain 14 is inflated, it is
desirable for the inflation fluid in the curtain to be
maintained at a desired pressure in order to help
prevent vehicle occupants from penetrating through the
curtain. By "penetrating through," it is meant that
the pressure of the inflation fluid in the inflatable

-14-

curtain is insufficient to prevent an occupant from
moving the first and second panels together upon
striking the curtain and the occupant thus essentially
strikes the side structure 16 of the vehicle 12.
Initially, the inflatable curtain 14 is inflated to a
desired pressure, preferably between 149-163
kilopascals (kPa) absolute (between about 48-62 kPa
gauge) , within 20-30 milliseconds (ms) . Once inflated,
the inflatable curtain 14 is maintained at the desired
pressure (14 9-163 kPa absolute) throughout about the
first 100 milliseconds of inflation. Thereafter, the
inflation pressure may decay due to leakage or cooling.
Once inflated, the inflation pressure should remain
above a second desired pressure, preferably 125 kPa
absolute, for a predetermined period of time,
preferably at least about the first 5-7 seconds of
inflation. This second desired pressure may, however,
be higher or lower depending upon factors such as the
volume of the inflatable curtain 14 and the thickness
of the curtain when inflated.

Preferably, the inflatable curtain 14, initially,
is inflated to the desired pressure (149-163 kPa
absolute) within 20-30 milliseconds. In order to
achieve the desired pressure in the inflatable curtain

14 when the curtain is initially inflated, the inflator
24 must deliver a given amount of inflation fluid
according to the volume of the curtain. A preferred
inflator 24 is a stored gas inflator containing
compressed helium at about 6250 psig. In order to
achieve the desired pressure in an inflatable curtain
having a volume ranging between 12-50 liters, the
preferred inflator must deliver between 0.7-3.3 moles
of helium gas. For example, an inflatable curtain
having a volume of about 2 7 liters may require about
2.2 moles of helium gas in order to achieve a desired
inflation pressure.

Those skilled in the art will recognize that the
amount of inflation fluid delivered to the inflatable
curtain 14 must account for losses due to leakage,
curtain stretching/expansion, etc. This is especially
true when using helium inflation fluid because helium,
having a low atomic weight, flows more easily through
leakage points than other gasses. Therefore, leakage
and other losses are taken into account when sizing the
inflator 24. Also, special care may be taken to seal
the inflatable curtain 14 and any connections between
the curtain and the inflator 24 and/or fill tube 22
where leakage may occur.

It is also desirable for the front and rear
portions 64 and 66 of the inflatable curtain 14 to
inflate away from the roof 18 evenly between the
forward and rearward portions 64 and 66 along the
length of the curtain. It is further desirable for the
pressure and temperature of the inflation fluid in the
forward portion 64 of the inflatable curtain 14 to be
the same as the pressure and temperature, respectively,
of the inflation fluid in the rearward portion 66 of
the inflatable curtain throughout the predetermined
period of time, i.e., at least the first 5-7 seconds of
inflation. According to the present invention,
therefore, the fill tube 22 is constructed such that
the inflatable curtain 14 inflates generally evenly
between the forward and rearward portions 64 and 6 6
along the length of the curtain. The fill tube 22 is
also constructed such that the inflation fluid in the
curtain 14 has generally the same temperature and
generally the same pressure in the forward and rearward
portions 64 and 66 along the length of the curtain
throughout the predetermined period of time.

As illustrated in Fig. 5, the second portion 32 of
the fill tube 22 includes a plurality of outlet
apertures 100 that are spaced along the length of the

second portion 32 of the fill tube. The outlet
apertures 100 are arranged in groups of apertures 102,
each of which includes a predetermined number of
apertures spaced along a line that extends along a
portion of the length of the fill tube 22 . The groups
of apertures 102 are spaced a predetermined distance
apart from each other along the length of the fill
tube 22.

In the illustrated embodiment, the fill tube 22
preferably has an outside diameter of about
1-5-.-8-7-5- mi-l-lime t ers— and- -a - wall- thickness -of- about
0.71 millimeters. The outlet apertures 100 are
preferably pierced holes having a diameter in the range
of about 7.0-9.0 millimeters. The outlet apertures 100
may, however, have a different geometry in order to
produce a desired effect, such as directing the
inflation fluid in a certain direction from the fill
tube 22. The outlet apertures 100 in each of the
groups of apertures 102 are spaced apart from each
other about 12 . 0 millimeters center to center.

In the illustrated embodiment, a first group of
apertures 110 includes three outlet apertures 100. The
first group of apertures 110 is spaced a distance
indicated at 112 from the inflator 24. The

-18-

distance 112 is preferably about 490 millimeters. A
second group of apertures 120 includes five outlet
apertures 100. The second group of apertures 120 is
spaced a distance indicated at 122 from the first group
of apertures 110. The distance 122 is preferably
about 144 millimeters. A third group of apertures 13 0
includes eight outlet apertures 100. The third group
of apertures 130 is spaced a distance indicated at 132
from the second group of apertures 12 0. The
distance 132 is preferably about 485 millimeters. A
fourth group of apertures 14 0 includes eight outlet
apertures 100. The fourth group of apertures 140 is
spaced a distance indicated at 142 from the third group
of apertures 130. The distance 142 is preferably about
8 5 mi 1 1 imet ers .

It will be recognized by those skilled in the art
that the cross-sectional flow area of the fill tube 22,
the number of groups of apertures 102, the number of
apertures 10 0 in each group, and the spacing of the
groups may vary depending upon the construction of the
inflatable curtain 14. For example, in an inflatable
curtain 14 extending between the A and B pillars 80
and 84, there may be fewer groups of apertures 102 and
fewer outlet apertures 100 in the groups. Conversely,

in a curtain extending between the A and D pillars 8 0
and 86, there may be more groups of apertures 102 and
more outlet apertures 100 in the groups.

The distances between the groups of apertures 102
and the number of outlet apertures 100 in each group of
apertures are predetermined in order to help ensure
that the forward and rearward portions 64 and 66 of the
inflatable curtain 14 are inflated evenly along the
length of the curtain. As illustrated in Fig. 5, the
rearward portion 66 has a smaller volume than the
forward portion 64 . The inflation fluid is directed
into the rearward portion 64 by the first group of
apertures 110. The number and spacing of the outlet
apertures 100 in the first group of apertures 110 is
predetermined such that the volume of inflation fluid
delivered into the rearward portion 66 inflates the
rearward portion to a desired pressure in a desired
time .

The forward portion 64 of the inflatable curtain
14 has a considerably larger volume than the rearward
portion 66. Thus, the volume of inflation fluid
delivered into the forward portion 66 must be
considerably larger than the volume delivered into the
rearward portion 64 . The number and spacing of the

outlet apertures 100 in the second, third and fourth
groups of apertures 120, 130, and 140 is predetermined
such that the volume of inflation fluid delivered into
the forward portion 64 inflates the forward portion to
the same desired pressure in the same time as the
rearward portion 66. This helps to ensure that the
forward and rearward portions 64 and 66 will inflate
evenly along the length of the inflatable curtain 14.

When the inflator 24 is actuated, there is a large
pressure differential between the compressed inflation
fluid in the inflator and the gas occupying the fill
tube 22. As a result, the inflation fluid accelerates
from the inflator 24 into the fill tube 22, reaching a
supersonic velocity. Once inside the fill tube 22, the
inflation fluid slows to a velocity below supersonic
speed as pressure builds in the fill tube. As pressure
rises in the fill tube 22, a large pressure
differential is created between the tube and the
inflatable curtain 14. This causes the inflation fluid
to reach a supersonic velocity as the fluid enters the
inflatable curtain 14 through the outlet apertures 100.

By "supersonic velocity", it is meant that the
velocity is above that of the speed of sound in a given
medium. For example, based on known principles of

gasses, the speed of sound of helium will be a given
velocity at a given temperature. Thus, a supersonic
velocity of helium at the given temperature would be
above the given velocity.

When the inflation fluid reaches a supersonic
velocity as it enters the fill tube 22 from the
inflator 24, a shock wave is created, which propagates
back and forth along the length of the tube . As the
shock wave propagates along the fill tube 22, fluid
temperatures at the end of the tube can reach maximum
temperatures in the range of 1000 - 1750 degrees Kelvin .
These high fluid temperatures are a result of adiabati
compressive heating of air that is in the fill tube 22
prior to actuation of the inflator 24 and isentropic
heating of the helium and air gas mixture as the shock
wave passes through the fluid media in the tube. Also
as the inflation fluid passes through the fill tube 22
the fluid gains heat thermodynamically from the tube,
which results in higher pressures in the inflatable
curtain 14 for a given amount of inflation fluid.

For purposes of the present invention, ambient
temperature is defined as 295° K, which is equal to
about 22° C or 71.6° F. As the inflation fluid enters
the inflatable curtain 14, the fluid quickly cools to

temperature just above the ambient temperature in which
the inflatable curtain 14 is deployed. This helps to
ensure that the desired pressure of the inflation fluid
in the inflatable volume 58 of the inflatable curtain
14 is maintained. The temperature of the inflation
fluid in the inflatable curtain 14, being just above
ambient temperature, will be less susceptible to
pressure loss due to thermodynamic heat loss. For
example, if the inflation fluid in the inflatable
curtain 14 was at a significantly higher temperature
than the ambient temperature, the inflation fluid
pressure in the curtain would decrease as the fluid is
cooled.

The above-listed results are achieved by using
helium in conjunction with the above described fill
tube construction to inflate the inflatable curtain 14.
The use of . the pressurized helium inflation fluid is
thus critical to the present invention. In the
illustrated embodiment, the inflatable curtain 14 has a
volume of about 27 liters. Based on the known physical
properties of helium, it was determined that about 2.2
moles of helium are required to inflate the inflatable
curtain 14 to the initial required pressure of about
149-163 kPa absolute. As stated above, it was also

known that the inflatable curtain 14 must be inflated
initially to the inflated position (Fig. 2) and to the
desired pressure within about 20-30 milliseconds.

Knowing these requirements, the inflator 24 and
fill tube 22 were sized so as to provide the helium
inflation fluid to the inflatable curtain 14 to inflate
the curtain initially to the desired pressure (149-163
kPa absolute) in the required time (20-30 ms) . In the
illustrated embodiment, the inflator 24 stores the
helium at about 6250 psig and the fill tube 22 is sized
in order to deliver the inflation fluid at a molar flow
rate sufficient to fill the inflatable curtain 14 to
the required pressure in the required amount of time.
In sizing the fill tube 22, the cross- sectional flow
area of the tube and the number of apertures 10 0 are
selected to provide the amount of inflation fluid
required to inflate the inflatable curtain 14 to the
desired pressure in the required time. Also, in sizing
the fill tube 22, the outlet apertures 100 were
numbered, grouped, and spaced in order to inflate the
inflatable curtain 14 evenly along the length of the
curtain. The apparatus 10, thus configured, would
inflate the inflatable curtain 14 to the desired
pressure evenly along the length of the inflatable

-24-

curtain 14, within the required amount of time (20-30
ms ) .

The cross-sectional flow area of the fill tube 22
is also sized so as to cause the helium inflation fluid
5 to maintain supersonic velocity in the fill tube during

deployment of the inflatable curtain 14 . As stated
above, the helium inflation fluid gains heat through
compressive heating of the air in the fill tube 22,

^1 shock wave propagation/oscillation along the length of

111

10 the fill tube, and thermodynamic heat transfer from the

p tube . As the helium ilif latToh fluid enters "the

61 inflatable curtain 14, the fluid quickly cools to a

^ temperature just above ambient temperature which, as

\ % \ stated above, helps to prevent pressure loss in the

it 15 curtain.

These results are facilitated through the use of
the helium inflation fluid in combination with the
described fill tube 22 construction. Inflation fluids
other than helium do not produce the above -listed
20 results, even if used in conjunction with the disclosed

fill tube construction. Helium, having a low molecular
weight, has a relatively high sonic flow rate compared
to other gasses. Thus, at a given temperature, helium
will flow through the fill tube and into the inflatable

curtain 14 faster than a gas having a higher molecular
weight. This allows the required amount of helium
inflation fluid to be delivered via the stored gas
inflator 24. Other gasses, having low sonic flow rates
compared to helium, would not produce the required flow
into the inflatable curtain 14 to inflate the device to
the required pressure in the required time without some
form of augmentation, such as added heat. Gasses other
than helium, used in a stored gas inflator in
conjunction with a fill tube constructed according to
the present invention, would thus be incapable of
achieving the desired results of inflating the
inflatable curtain 14 to the desired pressure in the
required time.

Also, both the critical temperature of helium (-
267° C) and the critical pressure of helium (33.8 psia)
are low as compared to other gasses. This helps to
ensure that the inflation fluid will remain in a
gaseous state throughout inflation. Other gasses,
having higher critical temperatures and pressures may-
require augmentation, such as added heat, in order to
ensure that the inflation fluid will remain in a
gaseous state throughout inflation.

-26-

Creation of the shock wave results in the heating
of the helium inflation fluid in the fill tube 22. The
properties of helium result in a better absorption of
thermal energy from the surrounding hardware, e.g. the
fill tube 22, for equivalent molar flow rates as
compared to other gasses . Thus, as the helium
inflation fluid passes through the fill tube 22, it
gains more heat than would other gasses. The helium
inflation fluid also loses heat quickly when it enters
the inflatable curtain 14 and quickly cools to a
temperature just above ambient temperature. Thus, the
inflatable curtain 14 will experience a smaller amount
of pressure loss over time due to cooling of the helium
inflation fluid. As a result, the use of the helium
inflation fluid results in more uniform pressure within
the desired range during at least the initial 5-7
seconds of inflation of the inflatable curtain 14.

Exemplary of the benefits gained through the use
of helium in an apparatus 10 constructed in accordance
with the present invention, the following compares
argon, which is a known inflation fluid, to helium.
The sonic flow rate of a gas is determined according to
the following equation:

c= (kG c RT) *

where :

c = sonic flow rate of the gas;

k = ratio of specific heats of the gas (C p /C v ),
where C p is the specific heat at constant
pressure and C v is the specific heat of the
gas at constant volume,
(For He, k=1.66, for Ar, k=1.67);

G c = a constant;

R = gas constant of the gas

(He = 386.3, Ar = 38.7); and

T - temperature of the gas

Based on the above-listed equation, it can be seen
that, at a given temperature, the values for k, G C/
and T are essentially equal for both helium and argon.
The only difference in the equations for helium and
argon is that the gas constant, R, for helium is about
ten times that of argon. Thus, at a given temperature,
helium has a sonic flow rate of about (10)*, or 3.16
times faster than argon. Thus, based on the equation
listed above, in order to increase the sonic flow rate
of argon to equal that of helium, the argon would need
to be heated to a temperature about ten times the
temperature of the helium.

Also, the critical temperature and critical
pressure of argon (-122° C, 705 psia) is much higher
than helium (-267° C, 33.8 psia). Thus, in order to
use argon to inflate the inflatable curtain 14 to the

-28-

required pressure in the required time, the argon must
be heated to ensure that the argon remains above the
critical temperature in order to remain in a gaseous
state throughout inflation. This is typically done by
5 augmentation, wherein the inflator includes a

pyrotechnic material that adds heat to the inflation
fluid. In providing inflation fluid at a higher
temperature, however, the inflation fluid would be
'41 delivered to the inflatable curtain 14 at a temperature

4-« 10 substantially higher than ambient temperature. As a

^ result, the inflatable curtain 14 would experience

pressure loss as the inflation fluid cools towards

j?j ambient temperature.

RJ

hj The above -listed results were verified by testing

o

m 15 an apparatus constructed in accordance with the

apparatus 10 of the illustrated embodiment. The tests
were performed by inflating a 27 liter inflatable
curtain 14 with 2.2 moles of helium stored at
about 6250 psig in the inflator 24. The helium
20 inflation fluid was delivered to the inflatable

curtain 14 via the fill tube 22, which was constructed
in accordance with dimensions about equal to those
listed above.

According to the testing procedure, the inflatable
curtain 14 was inflated from an unfolded condition.
The inflatable curtain 14 therefore was not placed in a
stored condition in the housing 26. During inflation,
inflation fluid pressure in the inflatable curtain was
monitored and recorded. The recorded data is
illustrated in Figs. 15-18.

Fig. 15 illustrates the inflation pressure of the
inflatable curtain 14 during the first 100 milliseconds
of inflation. As shown in Fig. 15, the inflatable
curtain 14 is inflated to about 14~6 kPa absolute at
2 0 milliseconds and about 157 kPa absolute at
30 milliseconds. The apparatus 10 thus inflates to
well within the desired pressure range (149-163 kPa
absolute) within the desired initial time period (20-30
ms) .

Those skilled in the art will recognize that some
of the inflation fluid pressure may be lost due to the
work that the inflation fluid must perform in deploying
the inflatable curtain 14 from a stored condition in
the housing 26. The work can be attributed to opening
the housing 2 6 (Fig. 1) and moving the inflatable
curtain 14 to the deployed position (Fig. 2) .
Therefore, the inflation pressures experienced during

the testing procedure may be slightly higher than thos
actually experienced when deploying the inflatable
curtain 14 from the stored position. Such losses,
however, are not large enough to reduce the inflation
pressure of the inflatable curtain 14 to a pressure
outside the desired inflation pressure range.

Fig. 16 illustrates the inflation pressure of the
inflatable curtain during the first six seconds of
inflation time. As illustrated in Fig. 16, the
inflatable curtain 14, once inflated to a pressure at
or above 14 9 kPa absolute, is maintained at or above
14 9 kPa absolute through the first 3.5 seconds of
inflation. Thereafter, the inflatable curtain 14 is
maintained at or above about 14 0 kPa absolute
throughout the first six seconds of inflation time.
Thus, once inflated, the inflatable curtain 14 is
maintained well within the desired pressure ranges of
149-163 kPa absolute for the first 100 milliseconds,
and above 125 kPa absolute for at least the first 5-7
seconds of inflation.

A similar test procedure was also performed with
similar apparatus 10 in order to monitor inflation
fluid temperature during deployment of the inflatable
curtain 14 . The data recorded during this procedure i

illustrated in Figs. 17 and 18. As illustrated in
Fig. 17, once inflated (20-30 ms) , the inflation fluid
temperature in the inflatable curtain 14 fluctuated
generally between 290-330° K. At about
100 milliseconds, inflation fluid temperatures level
out to about 305° K (about 32° C or 86° F) , just above
ambient, and thereafter level out to about 2 95° K (about
22° C or 71.6° F) , about ambient, throughout the six
second curtain deployment interval (see Fig. 18) . By
"just above ambient," it is meant that the temperature
is preferably within about 10-15° C above ambient. The
inflatable curtain 14 is thus maintained at the desired
temperature (about ambient) for a substantial portion,
i.e., all but 100 milliseconds or about 98.3% of the
initial six seconds of curtain inflation.

In determining the distances between the groups of
apertures 102 and the number of outlet apertures 100 in
each group of apertures, those skilled in the art will
recognize that it is desirable to simulate the
performance of a proposed inflatable curtain 14 and
fill tube 22 construction. This can be accomplished by
creating a computer-generated model that allows the
performance of the curtain/fill tube construction to be
monitored at various points in the curtain. The use of

m m

-32-

a computer-generated model also allows the design to be
repeatedly evaluated and modified in order to achieve
the desired performance without undergoing the time and
expense of physical testing. One type of such a
computer generated model is a two-dimensional
computational fluid dynamics (CFD) model.

Using two-dimensional CFD modeling, the
three-dimensional inflatable curtain 14 illustrated in
Figs. 1-5 is modeled by the model curtain 150
illustrated in Fig. 6. The model curtain 150 is
designed to model a curtain having a volume of about 2 7
liters and an inflator 152 containing about 2.2 moles
of compressed helium. The model curtain also includes
a fill tube 154 and a non-inflatable portion 156. The
non- inflatable portion 156 divides an inflatable
volume 160 of the model curtain 15 0 into a forward
portion 162 and a rearward portion 164. The locations
of the first , second, third, and fourth groups of
apertures in the fill tube 154 of the model curtain 150
are indicated at 170, 172, 174, and 176, respectively.
It should be noted that the two-dimensional CFD model
assumes zero leakage, zero material stretching, and
zero loss due to work in moving the model curtain 15 0
from a stored position to the deployed position.

The use of the two-dimensional CFD model allows
for monitoring the pressure and temperature of the
inflation fluid at locations in the model curtain 150
during inflation of the model curtain. As illustrated
in Fig. 6, the pressure and temperature of the
inflation fluid is monitored in the rearward
portion 164 at first and second locations 180 and 182,
respectively. The pressure and temperature of the
inflation fluid is monitored in the forward portion 162
at third and fourth locations 184 and 186,
respectively. The pressure and temperature of the
inflation fluid during inflation of the model
curtain 15 0 can thus be recorded in order to evaluate
the performance of the construction for which the model
was developed.

Figs. 7a, 7b, 8a and 8b illustrate the performance
of the model curtain 150 as constructed in accordance
with the illustration of Fig. 6. Figs. 7a and 7b
illustrate the pressure of the inflation fluid during
inflation of the model curtain 150. In Figs . 7a
and 7b, the solid line 200 represents the pressure in
the forward portion 162 of the model curtain 150
measured by averaging the readings taken at
locations 184 and 186. The dashed line 202 represents

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the pressure in the rearward portion 164 of the model
curtain 150 measured by averaging the readings taken at
locations 180 and 182 . As shown in Fig . 7a, there is
about a 25-50 kilopascals difference between the
5 pressure of the inflation fluid in the forward portion

162 of the model curtain 15 0 and the pressure of the
inflation fluid in the rearward portion 164 (Fig . 6 ) of
the model curtain during the first eight to ten

B

•jn milliseconds of inflation time. Thereafter, the

w

4* 10 pressures in the forward and rearward portions 162 and

H 16^4 become the same. "Thus, the" pressure of the

yl inflation fluid is generally the same in the forward

and rearward portions 162 and 164 of the model curtain
\l\ 150 during initial inflation of the curtain. As

fesr

15 illustrated in Fig. 7b, the pressure in the forward and

rearward portions 162 and 164 remain about the same at
least through the first six seconds of inflation .

As viewed in Fig. 7a, the model curtain 150
inflates to about 225 kPa absolute in the initial 20-30

2 0 milliseconds of inflation. This corresponds to about

124 kilopascals gauge, which would appear to be
substantially higher than the desired inflation
pressure. As stated above, however, leakage, material
stretching, and work losses are not included in the

two-dimensional CFD model. In reality, these losses,
especially leakage, may typically account for up to a
30-40% pressure loss, depending on the construction of
the apparatus. This would bring the inflation pressure
in the model curtain 150 down to about 74-8 6
kilopascals .

Figs. 8a and 8b illustrate the temperature of the
inflation fluid during inflation of the model
curtain 150. The solid line 204 represents the
temperature in the forward portion 162 of the model
curtain i _ 50 measured" by averaging "the readings taken at
locations ' 184 and 186. The dashed line 206 represents
the temperature in the rearward portion 164 of the
model curtain 15 0 measured by averaging the readings
taken at locations 180 and 182. As shown in Fig. 8a,
there is only about a 25-125 degrees Kelvin difference
between the temperature of the inflation fluid in the
forward portion 162 of the model curtain 15 0 and the
temperature of the inflation fluid in the rearward
portion 164 of the model curtain during the first five
milliseconds of inflation time. Thereafter, the
temperatures of the inflation fluid in the forward and
rearward portions 162 and 164 are within about 20
degrees Kelvin. Thus, the temperature of the inflation

fluid is generally the same in the forward and rearward
portions 162 and 164 of the model curtain 150 during
initial inflation of the curtain. As shown in Fig. 8b,
the temperature of the inflation fluid in the forward
and rearward portions 162 and 164 remains about the
same at least through the first six seconds of
inflation.

Fig. 9 illustrates a model curtain 250 modeled
after an inflatable curtain construction that is known
in the art. The model curtain 250 has the same
characteristics as the model curtain 150 (Fig. 6),
except that the fill tube 22 is omitted from the model
curtain 250 (Fig. 9) and inflation fluid is directed
directly into the curtain by an inflator 252. Thus,
the inflation fluid passes from a rearward portion 254
of the model curtain 250 to a forward portion 260 of
the curtain via passages 256 adjacent a non-inflatable
area 258 of the curtain. Figs. 10 and 11 illustrate
the performance of the model curtain 250.

Fig. 10 illustrates the pressure of the inflation
fluid during inflation of the model curtain 250. The
solid line 2 62 represents the pressure in the forward
portion 260 of the model curtain 250. The dashed line
2 64 represents the pressure in the rearward portion 2 54

-37-

of the model curtain 250. As shown in Fig. 10, there
is a large difference, up to about 250 kilopascals ,
between the pressure of the inflation fluid in the
forward portion 2 60 of the model curtain 2 50 and the
pressure of the inflation fluid in the rearward portion
254 of the model curtain during the first 12-15
milliseconds of inflation time. Thereafter, the
pressures become generally the same in the forward and
rearward portions 260 and 254.

Fig. 11 illustrates the temperature of the
-in-f-lat-ion- -fiuid-ve-rs-u-s- -time-.- -The— -sol-id- 1-ine 2 &6
represents the temperature in the forward portion 2 60
of the model curtain 250 during inflation of the model
curtain. The dashed line 268 represents the
temperature in the rearward portion 2 54 during
inflation of the model curtain. As shown in Fig. 10,
there is a large initial difference between the
temperature of the inflation fluid in the rearward
portion 254 and the temperatur.e of the inflation fluid
in the forward portion 260. The inflation fluid in the
rearward portion 254 initially jumps up to 800 degrees
Kelvin and decreases down to 450 degrees Kelvin in the
first two milliseconds, after which the temperature
gradually slopes down to 225-275 degrees Kelvin. The

-38-

inflation fluid in the forward portion 260 initially
jumps up to 400 degrees Kelvin and decreases down to
260 degrees Kelvin in the first two milliseconds, after
which the temperature gradually slopes upward to 4 50-
500 degrees Kelvin. It should be noted that, after the
first about 6 milliseconds of inflation, the
temperature difference between the forward and rearward
portions increases, and from 10 milliseconds to 50
milliseconds is at least 100 degrees Kelvin and grows
to upwards of 2 7 5 degrees Kelvin .

Fig . 12 iTlust rates a model curtain 350 mocleled
after another inflatable curtain construction that is
known in the art. The model curtain 350 has the same
characteristics as the model curtain 150 (Fig. 6) ,
except that the fill tube 22 is omitted from the model
curtain 350 (Fig. 12) . Instead, inflation fluid is
directed into the curtain 350 via a fabric tube 352
constructed of the curtain material and extending from
the curtain to an inflator 354. The tube 352 has a
diameter of about three inches. The inflation fluid
flows from the inflator 3 54 through the tube 3 52 and
into a rearward portion 356 of the model curtain 350.
The inflation fluid then flows through passages 358
adjacent a non- inflatable area 360 of the curtain into

a forward portion 362 of the curtain. Figs. 13 and 14
illustrate the performance of the model curtain 350.

Fig. 13 illustrates the pressure of the inflation
fluid during inflation of the model curtain 350. The
solid line 368 represents the pressure in the forward
portion 362 of the model curtain 350. The dashed line
370 represents the pressure in the rearward portion 356
of the model curtain 350. As shown in Fig. 13, the
pressure of the inflation fluid in the rearward portion
356 is between about 50-75 kilopascals higher than the
forward portion 3 62 of the model curtain 3 50 during the
first 3-4 milliseconds of inflation time. Thereafter,
the pressure is the same in the forward and rearward
portions 362 and 356 for an instant, i.e., the lines
368 and 370 cross. The pressure in the forward portion
362 then becomes about 20-60 kilopascals greater than
the pressure in the rearward portion 356 until about 20
milliseconds when the pressures become generally the
same .

Fig. 14 illustrates the temperature of the
inflation fluid during inflation of the model
curtain 350. The solid line 372 represents the
temperature in the forward portion 362 of the model
curtain 350. The dashed line 374 represents the

temperature in the rearward portion 3 56 of the model
curtain 3 50. As shown in Fig. 14, there is a large
initial difference between the temperature of the
inflation fluid in the rearward portion 356 of the
model curtain 350 and the temperature of the inflation
fluid in the forward portion 362. The temperature of
the inflation fluid in the rearward portion 356
initially jumps up to about 800 degrees Kelvin and
decreases down to about 400 degrees Kelvin in the first
two milliseconds, after which the temperature gradually
slopes down to 220-280 degrees Kelvin. The temperature
of the inflation fluid in the forward portion 362
initially jumps up to about 52 0 degrees Kelvin and
decreases down to about 480 degrees Kelvin in the first
three milliseconds, after which the temperature jumps
up to about 575 degrees Kelvin and levels off at
about 550 degrees Kelvin. It should be noted that,
after the first about 2 milliseconds of inflation, the
temperature difference between the forward and rearward
portions 362 and 356 increases, and from 5 milliseconds
to 50 milliseconds is at least 250-300 degrees Kelvin
difference .

From the above description of the invention, those
skilled in the art will perceive improvements, changes

#

+

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and modifications. Such improvements, changes and
modifications within the skill of the art are intended
to be covered by the appended claims.

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